Tri Bike Fit Calculator

Estimate triathlon aero position geometry from body measurements including saddle height, aerobar reach, frame size, and crank length.

Height (cm)

Inseam (cm)

Torso length (cm)

Arm length (cm)

Tab to move between fields

Saddle height (cm)

72.6

Frame size (cm)53.3

Effective top tube (cm)58.1

Saddle setback (cm)1.6

Aerobar reach (cm)55.1

Pad width (cm)20.2

Saddle-pad drop (cm)-5

Aerobar stack (cm)67.6

Crank length (mm)175

KOPS forward (cm)3.9

Hip angle (°)80

How to Use This Calculator

Measure and enter your Height, Inseam, Torso Length, and Arm Length in centimeters.
Review the recommended Saddle Height (BB to top) as your starting point.
Check Frame Size, Effective Top Tube, Aerobar Reach, and Aerobar Pad Width.
Use Saddle-Pad Drop and Hip Angle to assess your aero position comfort and power output.
Cross-reference these values with a professional bike fitter for final dialing.

How the result changes with Inseam (cm)

Height (cm): Your total standing height in centimeters.
Inseam (cm): Inside leg measurement from floor to crotch (stand barefoot against a wall).
Torso length (cm): Distance from the top of your hip bone (iliac crest) to the sternal notch at the base of your neck.
Arm length (cm): Measured from the acromion (shoulder point) to the center of the wrist with arm extended.

Saddle height (cm): Center of bottom bracket to top of saddle. Based on 88.5% of inseam for tri position.
Frame size (cm): Recommended seat tube length (center-to-top) for a triathlon/TT frame.
Effective top tube (cm): Horizontal distance from head tube center to seat post center.
Saddle setback (cm): Saddle position behind the bottom bracket. Tri bikes use minimal setback (0-3cm).
Aerobar reach (cm): Distance from saddle nose to aerobar pads.
Pad width (cm): Distance between aerobar pad centers. Narrower is more aerodynamic.
Saddle-pad drop (cm): Height difference between saddle top and aerobar pads. Negative means pads are lower.
Aerobar stack (cm): Height of aerobar pads above bottom bracket center.
Crank length (mm): Recommended crank arm length. Tri bikes often use slightly shorter cranks.
KOPS forward (cm): Knee-over-pedal-spindle: how far forward of the pedal spindle your knee is at 3 o'clock.
Hip angle (°): Estimated hip angle in aero position. Tri bikes target 75-85° for sustainable power.

Identify Input Parameters
4 parameters
Height (cm) = 175, Inseam (cm) = 82, Torso length (cm) = 58, Arm length (cm) = 63 = 4 input(s) provided
Calculate Saddle height
Saddle height = inseamCm * 0.885
72.6 = 72.6
Calculate Frame size
Frame size = inseamCm * 0.65
53.3 = 53.3
Calculate Effective top tube
Effective top tube = (torsoLengthCm + armLengthCm) * 0.48
58.1 = 58.1